Adolescence represents a period of heightened vulnerability to substance use disorders. Although a variety of psychological and sociological factors contribute to this vulnerability, relatively few data exist regarding the functioning of the adolescent reward system at a neurobiological level. In this proposal, we will focus on the structures associated with the human dopaminergic system. Previous work in both animals and humans has elucidated some of the computational algorithms that the dopamine system performs. A leading candidate, the reward prediction error model, postulates that dopamine is released in response to unexpected rewards, which then modulates learning at a behavioral and synaptic level. Recent functional magnetic resonance imaging (fMRI) data from our group and others supports this model. In this application, we propose to use fMRI to assay the reactivity of the reward system in the adolescent brain. Compared to an adult, adolescent decision making capacity appears immature. Developmental models of cognition, e.g. Piaget's, suggest that immature decision making in the adolescent results from a less sophisticated stage of cognitive operation. In contrast to a staged development framework, we propose to examine the biological functioning of the reward system. Although the prediction error model of dopamine release is well supported across a range of species, the functional consequences of the developmental trajectory of the dopamine system have been relatively unexplored. To our knowledge, no data exist on the functional attributes of the adolescent reward system. If the adolescent reward system operates differently than the adult's, then this will have obvious implications for judgment and decision making, independently of cognitive operations. To accomplish this broad goal, we propose three specific aims: 1) use fMRI to measure reward system responsiviry to changes in predictability of pleasant oral stimuli, and compare the responsivity in adults and adolescents; 2) use fMRI to measure the relationship of musical preference to reward system responses in adults and adolescents to see if the adolescent reward system is more active; and 3) use fMRI to measure how peer pressure affects preference related activity in the reward system of adolescents and adults to see if the adolescent reward system is more susceptible to peer influences.